1. Field of the Invention
The present invention relates to an organic electro-luminescence (EL) element used in a display device and, more particularly, to a method of packaging an organic EL element used in a display device.
2. Description of the Related Art
In an electro-luminescence (EL) element used for a display device, electric current applied to specific fluorescence or phosphorus can transform electricity into luminosity. According to the different materials used in the luminescent layer, EL elements are classified as organic and inorganic, wherein the organic EL element employs laminated organic layers and has the advantages of thin profile, light weight, high luminescent efficiency, and low driving voltage. However, as the duration of use increases, the probability of moisture and oxygen permeating the organic EL element also increases, causing detachment between the organic luminescent layer and the cathode electrode, cracking of the organic materials, and oxidation of the electrodes. As a result, a so-called ‘dark spot’, to which electricity is not supplied, is generated, decreasing luminescence and luminescent uniformity.
In order to prevent the internal space of the organic EL element from developing a high humidity condition, a sealing case is commonly used to package the glass substrate on which metal electrodes and the organic luminescent layer are completed. Also, in order to prolong the active lifetime, a desiccant is installed to absorb the moisture and impurities generated in the interior space, the water and oxygen permeating from the atmosphere, and the moisture generated from the outgassing caused by the bonding agent on the rim of the sealing case. Furthermore, various technologies of reducing the interior humidity, to solve the problem of the dark spot, are developed, such as forming photo-hardened resin on the glass substrate, plating metal oxide, fluoride or sulfide on the glass substrate, forming a water-resistance film on the glass substrate, and using an airtight case to package the organic EL element. Nevertheless, other problems, such as leakage current, crosstalk and oxide dissolution, are found to be solved.
As shown in FIG. 1, U.S. Pat. No. 5,882,761 discloses an organic EL element 10, which comprises a glass substrate 12, a sealing agent 14 of UV-curing resin formed on the rim of the glass substrate 12, and a sealing case 16 bonded to the glass substrate 12 by the sealing agent 14. Thus, the internal space formed by the glass substrate 12 and the sealing case 16 becomes an airtight container. Also, in the airtight container, the glass substrate 12 comprises a lamination body 20 that is formed by a cathode layer 26, an organic luminescent material layer 24 and an anode layer 22. Furthermore, a drying substance 28 is disposed on the bottom of the sealing case 16 and spaced from the lamination body 20 by an internal space 18 that is filled with dried inert gas. The drying substance 28 comprises a solid compound, such as BaO, CaO, CaSO4, and CaCl2, which chemically absorbs moisture and maintains its solid state.
However, the UV-curing resin used in the sealing agent 14 is epoxy resin that has good adhesion but poor resistance to moisture in the internal space 18 caused by outgassing of the sealing agent 14 and the permeation of water and oxygen from the atmosphere. This may compromise the luminescent properties of the organic EL element 10. Seeking to solve the above-mentioned problem, one method is to develop a new material for the sealing agent 14 to achieve good adhesion and good water/oxygen-resistance ability. Yet, in consideration of the thermal expansion coefficient match, the glass transition temperature and the contact angle, adequate material has yet to be developed for the sealing agent 14. The other method is to add a large number of BaO or CaO to the drying substance 28 to increase the moisture absorbency. Unfortunately, the moisture absorbency is limited when the thickness of the drying substance 28 exceeds a critical value. Thus, a new method of packaging the organic EL element solving the aforementioned problems is called for.